It is well known to use the back electromotive force generated by a spin motor of a disk drive apparatus to unload the read/write heads thereof when the disk drive apparatus (including the spin motor) is being powered down. For example, this feature is discussed in U.S. Pat. No. 4,371,903 to Lewis, issued Feb. 1, 1983.
In such a typical case, the motor windings used for driving the spin motor when drive current is applied thereto are the same windings which generate the back electromotive force used for unloading upon power down. Typically, with lap top disk drives using five volt power supplies (versus 50 volts approximately 20 years ago or 12 volts approximately four years ago), peak unload voltage generated in such a system is limited by the normal run back electromotive force constant (typically 2.5 to 3 volts in the case of a five volt power supply).
It will readily be seen that an increase in the generated peak unload voltage in the above-described situation would be highly advantageous. However, it must be assured that appropriate voltage headroom requirements are maintained during running of the spin motor.
Of more general interest are U.S. Pat. No. 4,933,785 to Morehouse et al., issued Jun. 12, 1990; U.S. Pat. No. 4,535,374 to Anderson et al., issued Aug. 13, 1985; U.S. Pat. No. 4,568,988 to McGinlay et al., issued Feb. 4, 1986; U.S. Pat. No. 4,638,383 to McGinlay et al., issued Jan. 20, 1987; U.S. Pat. No. 4,518,904 to MacLeod et al., issued May 21, 1985; U.S. Pat. No. 3,984,873 to Pejcha, issued Oct. 5, 1976; and the publication "Quantum Low Power Products: Go Drive-2 1/2-inch Hard Disk Drives-ProDrive Gem Series-3 1/2-inch Small Frame Devices--Technical Highlights", Sep. 1990.